Linux and the boot process

The BIOS launches a bootloader (generally found in the Master Boot Record of the first hard disk)

This bootloader (generally Grub) allows the user to choose a Linux kernel…

… which then boots.

A system administrator should know how to:

Configure Grub properly (EL6 and EL7) so that the Linux kernel can boot properly.

Configure the Linux boot process itself so that only the needed services and drivers are loaded. In EL6, this includes knowing about the SysV init process, runlevels and the role of the inittab. In subsequent releases of RHEL/CentOS (EL7 onwards), SysV is replaced by systemd.

Of course, the system administrator should also know how to reboot and shutdown the computer.